Identification of the first several nephrotic syndrome and focal segmental glomerulosclerosis (FSGS) genes has had a significant impact on the understanding of glomerular function and disease. However, It is clear that the known genes account for only a fraction of these diseases. Here our goal is further elucidation of the genetic basis of FSGS, using a database of over 2500 individuals assembled over the past eleven years. Specifically, we will perform mutational analysis of known FSGS genes in families with FSGS and in patients with sporadic FSGS. We will continue our ongoing ascertainment of families with FSGS as well as sporadic adult and pediatric cases. Mutational analysis of these known FSGS genes will further inform our understanding of the spectrum of mutations, inform genotype/phenotype relationships, provide further information regarding structure and function, and help clarify the utility of genetic testing. We will also aim to Identify new FSGS genes. Through genome-wide scans, we have identified several genetic regions that appear to harbor as yet unidentified FSGS genes. We will analyze genes within these disease-associated regions in order to identify disease-associated variation. We will continue to perform additional genome-wide scans in new, genetically informative families as they are ascertained. We will test the hypothesis that rare DNA sequence variants in critical podocyte/glomerulus genes contribute to the etiology of FSGS. We will resequence candidate genes in 300 FSGS cases and 300 controls and determine if rare deleterious variants in these genes are more common in cases. We will replicate positive results in independent sample sets. FSGS is a significant and growing cause of chronic kidney disease and kidney failure. FSGS is also a common consequence of a variety of primary conditions. These studies will help understand the underlying causes of this disease.